Phytochemical and functional analysis of horseradish (Armoracia rusticana) fermented and non-fermented root extracts.

Background: The roots of horseradish (Armoracia rusticana) are used for infections of respiratory airway and for urinary tract infections due to isothiocyanates (ITC), enzymatically formed during fermentation of glucosinolates by myrosinase.

Hypothesis/purpose: The present study aims to present a comprehensive overview on the phytochemical composition of A. rusticana roots, especially concerning isothiocyanates and respective glucosinolates. The complex flavonoid spectrum of the herbal material is reviewed. Published data on in vitro activity of horseradish extracts and isolated compounds are summarized. These data indicate well-established use of horseradish as an antibacterial remedy against bacterial infections of the airway and urinary tract.

Study Design: To answer the question if other compounds from A. rusticana beside ITC contribute to the antibacterial activity, non-targeted LC-MS studies were performed with fermented and non-fermented horseradish extracts, and detailed phytochemical profiles were established.

Results: Comparative investigations on the antibacterial activity indicated that only ITC-containing extracts and fractions exert antibacterial activity. The huge variety of non-ITC compounds do not significantly contribute to the antibacterial activity, but can be used for analytical characterisation and quality control of the herbal material. Detailed phytochemical analysis additionally revealed a variety of compounds, not described until now for horseradish roots: the flavonol glycosides kaempferol-3-O-β-d-xylopyranosyl-(1''' → 2'')-β-d-galactopyranoside, kaempferol-3-O-α-l-rhamnopyranosyl-(1''' → 6'')-β-d-glucopyranoside, kaempferol-3-O-β-d-glucopyranoside, Kaempferol-3-O-β-d-xylopyranosyl-7-O-β-d-glucopyranoside, Kaempferol-3-O-β-d-xylopyranosyl-(1'''' → 2''')-β-d-galactopyranoside-7-O-β-d-glucopyranoside, the oxo-indole derivative spirobrassinin, the phenylthiazole 2-methylsulfanyl-4-phenyl-4,5-dihydro-1,3-thiazole, a series of lysophophatidylethanolamine and 13 different N-phenylpropenoyl-L-amino acids.

Conclusion: The antibacterial effects of horseradish are only due to the presence of glucosinolates resp. the corresponding ITC, and the detailed overall composition of horseradish extracts has been reported.